1. Field of the Invention
This invention is directed to drilling rigs and to methods for erecting masts for mobile drilling rigs.
2. Description of Related Art
The a wide variety of rigs used in drilling and various wellbore operations are well known, and described, for example, in U.S. Pat. Nos. 3,340,938; 3,807,109; 3,922,825; 3,942,593; 4,269,395; 4,290,495; 4,368,602; 4,489,526; 4,569,168; 4,837,992; 6,634,436; 6,523,319; and 7,306,055. A variety of systems and methods for assembling and erecting a drilling rig are also known; and described for example in U.S. Pat. Nos. 2,993,570; 3,201,091; 3,262,237; 3,749,183; 4,221,088; 4,269,009; 4,292,772; 4,305,237; 4,478,015; 4,587,778; 4,630,425; and 4,932,175.
In many prior rigs and erection methods, rig components and structures used with a rig are raised by a crane and positioned on a rig's drill floor. Various problems and disadvantages are associated with using a crane. A crane is typically a large apparatus which is transported to a drilling site where it is assembled and/or made ready for lifting and locating rig components.
In addition, rig erection structures, apparatuses, and methods are disclosed in pending U.S. Applications co-owned with the present invention: U.S. application Ser. Nos. 12/074,258; 12/074,264; 12/074,232; and 12/074,270 all filed Feb. 29, 2008 and pending U.S. application Ser. No. 12/069,913 filed Feb. 13, 2008; Ser. No. 12/152,651 filed May 15, 2008; and Ser. No. 11/906,147 filed Sep. 28, 2007.
In certain known rig assembly methods, there is no clear path for a vehicle (e.g. a truck/trailer used for transporting a mast section) into or through the center of a rig substructure during rig assembly. Also, in certain known rig assembly methods, a mast (or part of it) cannot be brought to the substructure at normal truck height and the mast cannot be connected directly to the substructure from a truck. These problems are made worse when there is an obstruction, e.g. a relatively large well head or cellar, at well center in the path through the substructure. These deficiencies render these known rig assembly methods complex, inefficient, and time-consuming.